Amphiphilic block polymer ultralow-permeability agent and intelligent temporary plugging type water-based drilling fluid

ABSTRACT

An ultralow-permeability agent contains a structural unit provided by styryl hydrophobic monomer, maleic anhydride and acrylamide; the drilling fluid contains two or more of water, sodium bentonite, Pac-Lv, the ultralow-permeability agent, calcium carbonate, one-way plugging agent, white asphalt and barite which are stored in a mixed manner or independently stored. When the amphiphilic block polymer provided by the invention is used as the ultralow-permeability agent of the intelligent temporary plugging type water-based drilling fluid, the self-adaptive characteristic is realized; according to the amphiphilic block polymer, temporary plugging layer gaps formed in pore and throats by plugging materials in drilling fluid can be fully filled under the condition that the sizes and the distribution of the pore and throats of reservoirs are not required to be clear, so that the permeability of temporary plugging layer is greatly reduced, ultralow-permeability is realized.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to Chinese Application No.202010807707.9, filed on Aug. 12, 2020, entitled “Amphiphilic blockpolymer ultralow-permeability agent and intelligent temporary pluggingtype water-based drilling fluid”, which is specifically and entirelyincorporated by reference.

The invention relates to the technical field of oil and gas drilling, inparticular to an amphiphilic block polymer and an intelligent temporaryplugging type water-based drilling fluid.

BACKGROUND OF THE INVENTION

When a reservoir is drilled, the invasion of the solid phases and theliquid phases in the drilling fluid inevitably causes reservoir damage,even “kills” the reservoir, resulting in the failure of drilling anddevelopment of oil and gas reservoir.

The temporary plugging drilling fluid can quickly form a temporaryplugging layer with low permeability when the reservoir is drilled, theinvasion of the drilling fluid can be avoided to the maximum extent, andthe temporary plugging drilling fluid is a very ideal reservoirprotection drilling fluid, but the plugging material in the temporaryplugging drilling fluid must strictly match the reservoir requirements,and particularly the softening point and the particle size of thedeformable filling particles must strictly match the reservoirtemperature and the reservoir pore and throat size, so that a compacttemporary plugging layer with low permeability can be formed.

However, in most cases, the reservoir properties are complex, and thepore and throat size and distribution cannot be accurately known, sothat blindness exists in the selection of the filling particles, and theformulation design of the temporary plugging drilling fluid and theperformance of the drilling fluid are seriously influenced.

SUMMARY OF THE INVENTION

The invention aims to overcome the defects of the prior temporaryplugging drilling fluid technology and provide an amphiphilic blockpolymer and an intelligent temporary plugging water-based drilling fluidsuitable for the wide pore and throat size distribution reservoir,wherein the amphiphilic block polymer has the self-adaptivecharacteristic, can fully fill temporary plugging layer gaps formed inpore and throats by plugging materials in the drilling fluid under thecondition of not knowing the pore and throat sizes and the distributionof the reservoir, and can greatly reduce the permeability of thetemporary plugging layer.

In order to achieve the above object, the first aspect of the presentinvention provides an amphiphilic block polymer ultralow-permeabilityagent, which comprises structural unit A, structural unit B andstructural unit C, wherein the structural unit A is provided by styrylhydrophobic monomer, the structural unit B is provided by maleicanhydride, and the structural unit C is provided by acrylamide;

the content of the structural unit A is 32 wt % to 44 wt % based on thetotal weight of the ultralow-permeability agent; the content of thestructural unit B is 22 wt % to 28 wt %; the content of the structuralunit C is 33 wt % to 40 wt %.

The second aspect of the present invention provides an intelligenttemporary plugging type water-based drilling fluid which contains two ormore of the following components stored in a mixed manner orindependently:

water, sodium bentonite, Pac-Lv, the ultralow-permeability agent,calcium carbonate, one-way plugging agent, white asphalt and barite;

the ultralow-permeability agent is the amphiphilic block polymerultralow-permeability agent described in the first aspect.

Compared with the existing water-based drilling fluid technology, theintelligent temporary plugging type water-based drilling fluidcontaining the amphiphilic block polymer provided by the invention hasat least the following advantages:

(1) the amphiphilic block polymer provided by the invention can beself-assembled into nano-micron-scale deformable micelles, the micellescan form supermolecule aggregates with a wide particle size range byself-aggregation, and the temporary plugging layer gaps formed in poreand throats by plugging materials such as bridging particles can befully filled under the condition that the pore and throat size anddistribution of the reservoir are not required to be clear, so that thepermeability of temporary plugging layer is greatly reduced;

(2) the amphiphilic block polymer provided by the invention has a weaktackifying effect, has a gel-improving effect and can improve therheological property of the drilling fluid.

Additional features and advantages of the invention will be set forth inthe detailed description which follows.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The endpoints of the ranges and any values disclosed herein are notlimited to the precise range or value, and these ranges or values shouldbe understood to encompass values close to these ranges or values. Fornumerical ranges, each range between its endpoints and individual pointvalues, and each individual point value can be combined with each otherto give one or more new numerical ranges, and such numerical rangesshould be construed as specifically disclosed herein.

As described above, the first aspect of the present invention providesan amphiphilic block polymer comprising the structural unit A providedby styryl hydrophobic monomer, the structural unit B provided by maleicanhydride, and the structural unit C provided by acrylamide,

wherein the styryl hydrophobic monomer is selected from at least one ofstyrene, α-methyl styrene, 2-methyl styrene, 3-methyl styrene and4-methyl styrene;

the content of the structural unit A is 32 wt % to 44 wt % based on thetotal weight of the polymer; the content of the structural unit B is 22wt % to 28 wt %; the content of the structural unit C is 33 wt % to 40wt %.

As described above, the second aspect of the present invention providesa composition for producing the amphiphilic block polymer, whichcontains two or more of the following components stored in admixture orseparately:

amphiphilic block polymer, chain transfer agent, initiator, solvent andprecipitant;

wherein the content of the amphiphilic block polymer is 20 parts to 24parts by weight relative to 100 parts by weight of the solvent; thecontent of the chain transfer agent is 0.5 parts to 1 part by weight;the content of the initiator is 0.03 parts to 0.05 parts by weight; thecontent of the precipitant is 20 parts to 24 parts by weight; theamphiphilic block polymer is the amphiphilic block polymer according tothe first aspect.

It should be noted that the amphiphilic block polymer referred to in thesecond aspect and the following aspects of the present invention are allthe amphiphilic block polymer described in the first aspect of thepresent invention, and the description of the amphiphilic block polymerdescribed in the first aspect will not be repeated in the followingdescription of the present invention, and those skilled in the artshould not be construed as limiting the present invention.

Preferably, the chain transfer agent is selected from at least one of4-cyano-(thiobenzoic) pentanoic acid, 4-cyano-4-(thiobenzoyl) pentanoicacid, 4-cyanopentanoic acid dithiobenzoate.

Preferably, the initiator is selected from at least one ofazobisisobutyronitrile and azobisisoheptonitrile.

The kind of the solvent used in the composition for preparing theamphiphilic block polymer according to the present invention may bevarious known in the art, and preferably, the solvent is selected fromat least one of tetrahydrofuran and dimethylformamide.

Preferably, the precipitant is selected from at least one of petroleumether and n-hexane.

The sources of the raw materials for the amphiphilic block polymer, thechain transfer agent, the initiator, the solvent and the precipitant arenot particularly limited in the present invention, and variouscommercially available products can achieve the aforementioned object ofthe present invention.

As previously mentioned, the third aspect of the present inventionprovides a method for preparing the amphiphilic block polymer accordingto the first aspect, the method comprising: in the presence ofprotective gas,

(1) the weight ratio of the dosage is 1:0.02-0.04:0.004-0.008 of thestyryl hydrophobic monomer I, the chain transfer agent contact with theinitiator to carry out the first reaction to obtain the firstintermediate;

(2) in the presence of a solvent, contacting the first intermediate withthe styryl hydrophobic monomer II, maleic anhydride, acrylamide and theinitiator to perform the second reaction to obtain the secondintermediate, wherein the first intermediate, the styryl hydrophobicmonomer II, the maleic anhydride and the acrylamide are used in theweight ratio of 1:2.9-3.5:2.5-3.0:4.0-4.9;

(3) contacting the second intermediate with the precipitant to effectprecipitation;

the styryl hydrophobic monomer I and the styryl hydrophobic monomer IIprovide the structural unit A of the amphiphilic block polymer asdescribed in the first aspect above. That is, in the aforementionedpreparation method of the present invention, the styryl hydrophobicmonomer is added to the reaction system in at least two portions.

In the present invention, the protective gas is preferably nitrogen.

Preferably, the weight ratio of the first intermediate, the solvent andthe initiator is 1: 90-110:0.02-0.04.

Preferably, the weight ratio of the second intermediate to theprecipitant is 1:0.83-1.2.

Preferably, in step (1), the conditions of the first reaction at leastsatisfy: the temperature is 40-80° C., and the time is 16-24 h; morepreferably, the conditions of the first reaction at least satisfy: thetemperature is 50-70° C. and the time is 18-22 h.

Preferably, in step (2), the conditions of the second reaction at leastsatisfy: the temperature is 40-80° C., and the time is 16-24 h; morepreferably, the conditions of the second reaction at least satisfy: thetemperature is 50-70° C. and the time is 18-22 h.

Preferably, in step (3), the conditions for precipitation at leastsatisfy: the temperature is 25-28° C., and the time is 0.2-0.4 h; morepreferably, the conditions for precipitation at least satisfy: thetemperature is 25-26° C., and the time is 0.2-0.3 h.

In the present invention, according to a preferred embodiment, themethod for preparing the polymer comprises the steps of:

(1) according to the weight ratio of 1:0.02-0.04:0.004-0.008, weighingstyrene I, 4-cyano-(thiobenzoic) pentanoic acid andazobisisobutyronitrile, mixing in a three-neck flask, vacuumizing andfilling with protective gas (such as nitrogen), and stirring at 50-70°C. for 18-22 h to obtain the first material;

(2) mixing the first material with styrene II, maleic anhydride,acrylamide and azobisisobutyronitrile in the presence oftetrahydrofuran, wherein the weight ratio of the first material to thestyrene II to the maleic anhydride to the acrylamide to thetetrahydrofuran to the azobisisobutyronitrile is1:2.9-3.5:2.5-3.0:4.0-4.9:90-110:0.02-0.04, vacuumizing and filling withprotective gas (such as nitrogen), and stirring at 50-70° C. for 18-22 hto obtain the second material;

(3) mixing the second material with the temperature of not higher than28° C. with petroleum ether for precipitation, and drying theprecipitate, wherein the weight ratio of the second material to thepetroleum ether is 1:0.83-1.2.

Preferably, in the step (3), the drying conditions at least satisfy: thetemperature is 50-60° C., and the time is 4-6 h.

The inventor finds that the amphiphilic block polymer obtained by thepreparation method provided by the invention can be used as ahigh-quality ultralow-permeability agent, and further enables thedrilling fluid to have more excellent capability of reducing thepermeability of the temporary plugging layer.

As mentioned above, the fourth aspect of the present invention providesthe application of the amphiphilic block polymer according to the firstaspect described above in the drilling fluid.

In the invention, preferably, in the application, the polymer is used asan ultralow-permeability agent of the intelligent temporary pluggingwater-based drilling fluid.

In the application of the aforementioned polymer as theultralow-permeability agent of the intelligent temporary pluggingwater-based drilling fluid, the specific application method is thetechnology well known to those skilled in the art, the invention is notdescribed in detail herein, and those skilled in the art should not beconstrued as limiting the invention.

When the polymer of the present invention is used as anultralow-permeability agent of the intelligent temporary pluggingwater-based drilling fluid, the polymer can be self-assembled intonano-micron-scale deformable micelles, the micelles can formsupermolecule aggregates with a wide particle size range byself-aggregation, and the temporary plugging layer gaps formed in poreand throats by plugging materials such as bridging particles can befully filled under the condition of not determining the pore and throatsize and distribution of the reservoir, and the permeability oftemporary plugging layer is greatly reduced.

As described above, the fifth aspect of the present invention providesan intelligent temporary plugging water-based drilling fluid, whichcontains two or more of the following components stored in a mixedmanner or independently:

water, sodium bentonite, Pac-Lv, the ultralow-permeability agent,calcium carbonate, one-way plugging agent, white asphalt and barite;

the ultralow-permeability agent is the amphiphilic block polymer of thefirst aspect;

wherein the content of the sodium bentonite is 0.5 parts to 3 parts byweight relative to 100 parts by weight of water; the content of theultralow-permeability agent is 0.5 parts to 3 parts by weight; thecontent of the calcium carbonate is 2 parts to 8 parts by weight; thecontent of the one-way plugging agent is 1 part to 5 parts by weight;the content of the white asphalt is 1 part to 5 parts by weight; thecontent of the barite is 60 parts to 120 parts by weight; and,

the content of Pac-Lv is 1 wt % to 3 wt % based on the total weight ofthe drilling fluid.

Preferably, wherein the content of the sodium bentonite is 1 part to 2parts by weight relative to 100 parts by weight of water; the content ofthe ultralow-permeability agent is 1 part to 2 parts by weight; thecontent of the calcium carbonate is 4 parts to 6 parts by weight; thecontent of the one-way plugging agent is 2 parts to 3 parts by weight;the content of the white asphalt is 2 parts to 3 parts by weight; thecontent of the barite is 80 parts to 100 parts by weight; and,

the content of Pac-Lv is 1 wt % to 2 wt % based on the total weight ofthe drilling fluid.

The inventor found that the drilling fluid provided in the abovepreferred embodiment has a better ability to reduce the permeability ofthe temporary plugging layer, while having good rheological properties.

In the present invention, it should be noted that the water in thedrilling fluid is used as a solvent, and the water may be pure distilledwater and/or deionized water, or may be a mixed solvent containingdistilled water and/or deionized water, and those skilled in the artshould not be construed as limiting the present invention.

In the invention, the Pac-Lv is polyanionic cellulose for petroleumdrilling. Illustratively, the Pac-Lv may be a Pac-Lv offered by TianjinSamite chemical Co., Ltd under the designation SUMMIT.

Preferably, the one-way plugging agent is plant fiber or lignin.Illustratively, the lignin one-way plugging agent may be a commercialproduct supplied by Henan Mingtai chemical Co., Ltd under thedesignation DF-1.

As mentioned above, the sixth aspect of the present invention provides amethod for preparing the drilling fluid of the fifth aspect, the methodcomprising: mixing the components of the drilling fluid according to thefifth aspect.

Preferably, the mixing method comprises: mixing water, sodium bentonite,Pac-Lv, ultralow-permeability agent, calcium carbonate, one-way pluggingagent, white asphalt and barite in sequence.

According to a particularly preferred embodiment, the step of mixing thecomponents of the drilling fluid according to the fifth aspect abovecomprises:

(a-1) carrying out first mixing on water and sodium bentonite to obtainthe first mixed material;

(a-2) carrying out second mixing on the first mixed material and Pac-Lvto obtain the second mixed material;

(a-3) carrying out third mixing on the second mixed material andultralow-permeability agent to obtain the third mixed material;

(a-4) carrying out fourth mixing on the third mixed material and calciumcarbonate to obtain the fourth mixed material;

(a-5) carrying out fifth mixing on the fourth mixed material and one-wayplugging agent to obtain the fifth mixed material;

(a-6) carrying out sixth mixing on the fifth mixed material and whiteasphalt to obtain the sixth mixed material;

(a-7) carrying out seventh mixing on the sixth mixed material and bariteto obtain the seventh mixed material.

Preferably, the conditions of the first mixing, the second mixing, thethird mixing, the fourth mixing, the fifth mixing, the sixth mixing, andthe seventh mixing each independently satisfy: the stirring speed is8000-15000 rpm, and the mixing time is 3-20 min. More preferably, theconditions of the first mixing, the second mixing, the third mixing, thefourth mixing, the fifth mixing, the sixth mixing, and the seventhmixing each independently satisfy: the stirring speed is 10000-12000rpm, and the mixing time is 5-10 min.

In the present invention, there is no particular limitation on thepreparation method of the drilling fluid, and the preparation methodknown to those skilled in the art can be adopted, and the presentinvention is not described herein in detail, and the present inventionexemplifies a specific operation, and those skilled in the art shouldnot be construed as limiting the present invention.

The present invention will be described in detail below by way ofexamples.

In the following examples, unless otherwise specified, the experimentalinstruments and raw materials are commercially available.

Experimental Instruments

Six-speed viscometer: purchased from Qingdao Tongchun Petroleuminstruments Co., Ltd.

Drilling fluid water loss determinator: purchased from Qingdao TongchunPetroleum instruments Co., Ltd.

Raw Materials

Sodium bentonite: purchased from Hangzhou Pingshan Bentonite Co., Ltdunder the designation BT-1888.

Pac-Lv: purchased from Tianjin Samite chemical Co., Ltd under thedesignation SUMMIT.

Calcium carbonate: analytically pure.

One-way plugging agent: the lignin one-way plugging agent is purchasedfrom Henan Mingtai chemical Co., Ltd.

White asphalt: purchased from Beijing Peikangjiaye technologydevelopment Co., Ltd.

Barite: purchased from Lingshou Shengya mineral products Co., Ltd.

Raw materials for preparing the ultralow-permeability agent:

Styrene: purchased from Guangzhou Liqing trading Co., Ltd.

Maleic anhydride: purchased from Zibo Xinrong chemical technology Co.,Ltd.

Acrylamide: purchased from Jinan Hengcheng new materials Co., Ltd.

Chain transfer agent: 4-cyano-(thiobenzoic) pentanoic acid, availablefrom Annaiji chemical company.

Initiator: azobisisobutyronitrile, analytically pure.

Solvent: tetrahydrofuran, analytically pure.

Precipitant: petroleum ether, analytically pure.

In the following examples, the room temperature was 25±1° C. unlessotherwise specified.

In the following examples, the test methods for the properties involvedare as follows:

1. Evaluation of Basic Performance of Drilling Fluid

The method comprises the steps of taking 300 mL of drilling fluid,measuring the Apparent Viscosity (AV), the Plastic Viscosity (PV), theYield Point (YP), ϕ 6 and ϕ 3 of the drilling fluid by using thesix-speed viscometer, and measuring the API Filtration Loss (FLAN) ofbase fluid of the drilling fluid by using the drilling fluid water lossdeterminator.

The specific determination method is as follows: the drilling fluid tobe measured is poured into the viscosity measuring cup, and ϕ 600 and ϕ300 are sequentially read by using the six-speed viscometer at roomtemperature.

The AV is calculated as follows: AV=0.5×ϕ600

The PV is calculated as follows: PV=ϕ600-ϕ300

The Yield Point (YP) is calculated as follows: YP=0.51×(2×ϕ300-ϕ600)

Pouring the drilling fluid to be measured into the filter loss measuringcup, adding a sealing ring and covering the API filter paper, sealing itby using a filter screen, introducing nitrogen, measuring the totalvolume of the drilling fluid filtrate within 7.5 min at room temperatureunder the pressure of 0.69 MPa, and multiplying by 2 to obtain FLAN.

2. Evaluation of Plugging Effect of Drilling Fluid

5 kinds of artificial cores with similar porosity and differentpermeability are adopted, the permeability is respectively 150-250*10⁻³μm², 350-450*10⁻³ μm², 550-650*10⁻³ μm², 750-850*10⁻³ μm² and950-1050*10⁻³ μm² from low to high, and the plugging effect evaluationis respectively carried out on the artificial cores by using theintelligent temporary plugging water-based drilling fluid.

The plugging experimental conditions are as follows: the temperature isroom temperature, the pressure difference is 3.5 Mpa, the shearing rateis 100 s⁻¹, and the plugging time is 30 min. And respectively measuringthe core permeability before plugging and the core permeability afterplugging, calculating the plugging rate and the average plugging rate,and evaluating the intelligent plugging effect.

The core plugging rates with different permeabilities of the drillingfluid are calculated according to the following formula:

F ₁₅₀₋₂₅₀=(permeability after plugging−permeability beforeplugging)/permeability before plugging*100%;

F ₃₅₀₋₄₅₀=(permeability after plugging−permeability beforeplugging)/permeability before plugging*100%;

F ₅₅₀₋₆₅₀=(permeability after plugging−permeability beforeplugging)/permeability before plugging*100%;

F ₇₅₀₋₈₅₀=(permeability after plugging−permeability beforeplugging)/permeability before plugging*100%;

F ₉₅₀₋₁₀₅₀=(permeability after plugging−permeability beforeplugging)/permeability before plugging*100%.

The average plugging rate of the drilling fluid is calculated accordingto the following formula:

F _(average)=(F ₁₅₀₋₂₅₀ +F ₃₅₀₋₄₅₀ +F ₅₅₀₋₆₅₀ +F ₇₅₀₋₈₅₀ +F ₉₅₀₋₁₀₅₀)/5.

Preparation example 1: the preparation example is used for preparing theultralow-permeability agent AA-1

Weighing 5 g of styrene, 0.1 g of 4-cyano-(thiobenzoic) pentanoic acidand 0.02 g of azobisisobutyronitrile, mixing in a three-neck flask,vacuumizing, filling with nitrogen, and stirring at 60° C. for 20 h toobtain the macromolecular chain transfer agent;

mixing 2 g of macromolecular chain transfer agent with 6.24 g ofstyrene, 5.88 g of maleic anhydride, 8.52 g of acrylamide and 0.06 g ofazobisisobutyronitrile, dissolving in 200 mL of tetrahydrofuran,vacuumizing and filling with nitrogen, and stirring for 20 h at 60° C.to obtain the mixture I;

cooling the mixture I to room temperature, then mixing with 20 g ofpetroleum ether for precipitation, and drying at 50° C. for 4 h toobtain the ultralow-permeability agent AA-1.

Preparation example 2: the preparation example is used for preparing theultralow-permeability agent AA-2

Weighing 5 g of styrene, 0.2 g of 4-cyano-(thiobenzoic) pentanoic acidand 0.04 g of azobisisobutyronitrile, mixing in a three-neck flask,vacuumizing, filling with nitrogen, and stirring at 40° C. for 16 h toobtain the macromolecular chain transfer agent;

mixing 2 g of macromolecular chain transfer agent with 5.8 g of styrene,5 g of maleic anhydride, 9.8 g of acrylamide and 0.06 g ofazobisisobutyronitrile, dissolving in 200 mL of tetrahydrofuran,vacuumizing and filling with nitrogen, and stirring for 16 h at 40° C.to obtain the mixture II;

cooling the mixture II to room temperature, then mixing with 18.8 g ofpetroleum ether for precipitation, and drying at 50° C. for 4 h toobtain the ultralow-permeability agent AA-2.

Preparation example 3: the preparation example is used for preparing theultralow-permeability agent AA-3

Weighing 5 g of styrene, 0.15 g of 4-cyano-(thiobenzoic) pentanoic acidand 0.03 g of azobisisobutyronitrile, mixing in a three-neck flask,vacuumizing, filling with nitrogen, and stirring at 80° C. for 24 h toobtain the macromolecular chain transfer agent;

mixing 2 g of macromolecular chain transfer agent with 7 g of styrene,5.5 g of maleic anhydride, 8 g of acrylamide and 0.06 g ofazobisisobutyronitrile, dissolving in 200 mL of tetrahydrofuran,vacuumizing and filling with nitrogen, and stirring for 24 h at 80° C.to obtain the mixture III;

cooling the mixture III to room temperature, then mixing with 27 g ofpetroleum ether for precipitation, and drying at 50° C. for 4 h toobtain the ultralow-permeability agent AA-3.

Example 1: The Example is Used for Preparing the Intelligent TemporaryPlugging Water-Based Drilling Fluid BB-1

The formulation of the drilling fluid is specified in Table 1;

mixing the components of the drilling fluid at room temperature,specifically:

(a-1) carrying out first mixing on water and sodium bentonite to obtainthe first mixed material;

(a-2) carrying out second mixing on the first mixed material and Pac-Lvto obtain the second mixed material;

(a-3) carrying out third mixing on the second mixed material andultralow-permeability agent to obtain the third mixed material;

(a-4) carrying out fourth mixing on the third mixed material and calciumcarbonate to obtain the fourth mixed material;

(a-5) carrying out fifth mixing on the fourth mixed material and one-wayplugging agent to obtain the fifth mixed material;

(a-6) carrying out sixth mixing on the fifth mixed material and whiteasphalt to obtain the sixth mixed material;

(a-7) carrying out seventh mixing on the sixth mixed material and bariteto obtain the seventh mixed material;

the conditions for each mixing were the same: the time is 8 min, and thestirring speed is 11000 rpm.

And obtaining the intelligent temporary plugging water-based drillingfluid BB-1.

The rest of the examples were carried out in a similar manner to Example1, except that the formulations of the drilling fluids were differentfrom that of Example 1, the specific formulations are given in Table 1,and the rest were the same as Example 1, and the names of the drillingfluids prepared are given in Table 1.

TABLE 1 Com- Example Example Example Example parative 1 2 3 4 example 1Water/g 100 100 100 100 100 Sodium 2 1 3 2 2 bentonite/g Pac-Lv/g 2.13 23 2.13 2.12 Ultralow- permeability agent Dosage/g 1 2 3 0.5 / SpeciesAA-1 AA-2 AA-3 AA-1 / Calcium 5 4 8 5 5 carbonate/g One-way 3 2 5 3 3plugging agent/g White 2 3 5 2 2 asphalt/g Barite/g 100 80 120 100 100Name BB-1 BB-2 BB-3 BB-4 DBB-1

Test Example

1. Evaluation of Basic Performance of Drilling Fluid

The drilling fluids prepared in the above examples were tested for eachof their basic properties, and the present invention provides exemplarytest results for the following examples, as shown in Table 2.

TABLE 2 Number AV/mPa · s PV/mPa · s YP/Pa ϕ6 ϕ3 FL_(API)/mL Example 136.5 28 8.69 6 5 3.5 Example 2 39.5 29 10.73 8 6 2.5 Example 3 43.5 3211.75 11 9 1.7 Example 4 35.0 27 8.18 5 4 4.1 Comparative 32.5 27 5.62 32 7.2 example 1

From the above results, it can be seen that the ultralow-permeabilityagents were added to Examples 1 to 4, and the fluid loss of each examplewas lower than that of Comparative example 1 because of the pluggingeffect of the permeability agents. Meanwhile, the Yield Point, ϕ 6 and ϕ3 of Examples 1 to 4 was higher than that of Comparative example 1,which shows that the permeability agent has the gel-improving effect.

In the examples, Example 2 has highergel strength, lower fluid loss andsimilar viscosity than Example 1, while Example 2 in the formulationonly adds more permeability agent than Example 1, and the other treatingagents are added in the same amount, which indicates that the tackifyingeffect of the permeability agent is weak; in Example 3, the amount ofthe permeability agent is the largest, and more plugging materials,barite and the like are added, so that the viscosity is the highest, thegel strength is the largest, and the filtration loss is the lowest; inExample 4, the amount of the permeability agent is the smallest, theviscosity is lower, the gel strength is lower, and the fluid loss islarger.

2. Evaluation of Plugging Effect of Drilling Fluid

The drilling fluids prepared in the above examples were tested forplugging effect, respectively, and the present invention illustrativelyprovides the test results of the following examples, as shown in Table3.

TABLE 3 Number F₁₅₀₋₂₅₀ F₃₅₀₋₄₅₀ F₅₅₀₋₆₅₀ F₇₅₀₋₈₅₀ F₉₅₀₋₁₀₅₀ F_(average)Example 1 89.2% 88.0% 93.3% 89.7% 89.4% 89.9% Example 2 91.3% 89.9%93.4% 91.0% 90.9% 91.3% Example 3 96.6% 96.2% 96.9% 95.9% 96.2% 96.4%Example 4 83.1% 86.1% 88.8% 83.2% 85.1% 85.3% Comparative 72.1% 79.2%81.0% 73.1% 78.9% 76.9% example 1

From the results, it can be seen that Comparative example 1 does notcontain a permeability agent, only contains various plugging agents, andthe formed plugging layer has a certain plugging effect on rock coreswith different permeability; in Example 1, the ultralow-permeabilityagent is added, so that the plugging rate of the drilling fluid to therock cores with each permeability is improved by about 10%, whichindicates that the permeability agent can be self-adaptive to pore andthroats with different sizes, and the pores of the plugging layer areeffectively filled, so that the permeability is lower; by continuouslyincreasing the using amount of the permeability agent, the plugging rateof the rock cores in Example 2 and 3 is continuously increased to bemore than 90%; in Example 4, the amount of the permeability agent isless than that in Example 1, and the plugging effect is the worst in theexamples, but still better than that in Comparative example 1 withoutthe permeability agent.

In conclusion, when the amphiphilic block polymer provided by theinvention is used as the ultralow-permeability agent of the intelligenttemporary plugging water-based drilling fluid, the amphiphilic blockpolymer can be self-assembled into nano-micron-scale deformablemicelles, the micelles can self-aggregate to form supermoleculeaggregates with a wide particle size range, and the temporary plugginglayer gaps formed in pore and throats by plugging materials such asbridging particles and the like can be fully filled under the conditionthat the size and distribution of the pore and throats of reservoirs arenot required to be clear, the permeability of the drilling fluid isgreatly reduced, and the amphiphilic block polymer is weak in tackifyingeffect, has a gel-improving effect and can improve the rheologicalproperty of the drilling fluid.

The preferred embodiments of the present invention have been describedabove in detail, but the present invention is not limited thereto.Within the scope of the technical idea of the present invention, manysimple modifications can be made to the technical solution of thepresent invention, including various technical features being combinedin any other suitable way, and these simple modifications andcombinations should also be regarded as the disclosure of the presentinvention, and all fall within the scope of the present invention.

1. An amphiphilic block polymer ultralow-permeability agent, comprisingstructural unit A, structural unit B and structural unit C, wherein thestructural unit A is provided by styryl hydrophobic monomer, thestructural unit B is provided by maleic anhydride, and the structuralunit C is provided by acrylamide; the content of the structural unit Ais 32 wt % to 44 wt % based on the total weight of theultralow-permeability agent; the content of the structural unit B is 22wt % to 28 wt %; the content of the structural unit C is 33 wt % to 40wt %.
 2. The ultralow-permeability agent according to claim 1, whereinthe styryl hydrophobic monomer is selected from at least one of styrene,α-methyl styrene, 2-methyl styrene, 3-methyl styrene and 4-methylstyrene.
 3. The ultralow-permeability agent according to claim 1,wherein the ultralow-permeability agent is the permeability agentprepared by a method comprising the steps of: in the presence ofprotective gas, (1) the weight ratio of the dosage is1:0.02-0.04:0.004-0.008 of the styryl hydrophobic monomer I, the chaintransfer agent contact with the initiator to carry out the firstreaction to obtain the first intermediate; (2) in the presence of asolvent, contacting the first intermediate with the styryl hydrophobicmonomer II, maleic anhydride, acrylamide and the initiator to performthe second reaction to obtain the second intermediate, wherein the firstintermediate, the styryl hydrophobic monomer II, the maleic anhydrideand the acrylamide are used in the weight ratio of1:2.9-3.5:2.5-3.0:4.0-4.9; (3) contacting the second intermediate withthe precipitant to effect precipitation; the styryl hydrophobic monomerI and the styryl hydrophobic monomer II provide the structural unit A ofthe amphiphilic block polymer ultralow-permeability agent as describedin claim 1; the weight ratio of the second intermediate to theprecipitant is 1:0.83-1.2.
 4. The ultralow-permeability agent accordingto claim 3, wherein the chain transfer agent is selected from at leastone of 4-cyano-(thiobenzoic) pentanoic acid, 4-cyano-4-(thiobenzoyl)pentanoic acid, 4-cyanopentanoic acid dithiobenzoate; the initiator isselected from at least one of azobisisobutyronitrile andazobisisoheptonitrile; the solvent is selected from at least one oftetrahydrofuran and dimethylformamide; the precipitant is selected fromat least one of petroleum ether and n-hexane.
 5. Theultralow-permeability agent according to claim 3, wherein in step (1),the conditions of the first reaction at least satisfy: the temperatureis 40-80° C., and the time is 16-24 h; in step (2), the conditions ofthe second reaction at least satisfy: the temperature is 40-80° C., andthe time is 16-24 h.
 6. The ultralow-permeability agent according toclaim 4, wherein in step (1), the conditions of the first reaction atleast satisfy: the temperature is 40-80° C., and the time is 16-24 h; instep (2), the conditions of the second reaction at least satisfy: thetemperature is 40-80° C., and the time is 16-24 h.
 7. Theultralow-permeability agent according to claim 2, wherein theultralow-permeability agent is the permeability agent prepared by amethod comprising the steps of: in the presence of protective gas, (1)the weight ratio of the dosage is 1:0.02-0.04:0.004-0.008 of the styrylhydrophobic monomer I, the chain transfer agent contact with theinitiator to carry out the first reaction to obtain the firstintermediate; (2) in the presence of a solvent, contacting the firstintermediate with the styryl hydrophobic monomer II, maleic anhydride,acrylamide and the initiator to perform the second reaction to obtainthe second intermediate, wherein the first intermediate, the styrylhydrophobic monomer II, the maleic anhydride and the acrylamide are usedin the weight ratio of 1:2.9-3.5:2.5-3.0: 4.0-4.9; (3) contacting thesecond intermediate with the precipitant to effect precipitation; thestyryl hydrophobic monomer I and the styryl hydrophobic monomer IIprovide the structural unit A of the amphiphilic block polymerultralow-permeability agent as described in claim 1; the weight ratio ofthe second intermediate to the precipitant is 1:0.83-1.2.
 8. Theultralow-permeability agent according to claim 7, wherein the chaintransfer agent is selected from at least one of 4-cyano-(thiobenzoic)pentanoic acid, 4-cyano-4-(thiobenzoyl) pentanoic acid, 4-cyanopentanoicacid dithiobenzoate; the initiator is selected from at least one ofazobisisobutyronitrile and azobisisoheptonitrile; the solvent isselected from at least one of tetrahydrofuran and dimethylformamide; theprecipitant is selected from at least one of petroleum ether andn-hexane.
 9. The ultralow-permeability agent according to claim 7,wherein in step (1), the conditions of the first reaction at leastsatisfy: the temperature is 40-80° C., and the time is 16-24 h; in step(2), the conditions of the second reaction at least satisfy: thetemperature is 40-80° C., and the time is 16-24 h.
 10. Theultralow-permeability agent according to claim 8, wherein in step (1),the conditions of the first reaction at least satisfy: the temperatureis 40-80° C., and the time is 16-24 h; in step (2), the conditions ofthe second reaction at least satisfy: the temperature is 40-80° C., andthe time is 16-24 h.
 11. An intelligent temporary plugging typewater-based drilling fluid, wherein the drilling fluid contains two ormore of the following components stored in a mixed manner orindependently: water, sodium bentonite, Pac-Lv, theultralow-permeability agent, calcium carbonate, one-way plugging agent,white asphalt and barite; the ultralow-permeability agent is theamphiphilic block polymer ultralow-permeability agent according toclaim
 1. 12. The drilling fluid according to claim 11, wherein thecontent of the sodium bentonite is 0.5 parts to 3 parts by weightrelative to 100 parts by weight of water; the content of theultralow-permeability agent is 0.5 parts to 3 parts by weight; thecontent of the calcium carbonate is 2 parts to 8 parts by weight; thecontent of the one-way plugging agent is 1 part to 5 parts by weight;the content of the white asphalt is 1 part to 5 parts by weight; thecontent of the barite is 60 parts to 120 parts by weight.
 13. Thedrilling fluid according to claim 12, wherein the content of the sodiumbentonite is 1 part to 2 parts by weight relative to 100 parts by weightof water; the content of the ultralow-permeability agent is 1 part to 2parts by weight; the content of the calcium carbonate is 4 parts to 6parts by weight; the content of the one-way plugging agent is 2 parts to3 parts by weight; the content of the white asphalt is 2 parts to 3parts by weight; the content of the barite is 80 parts to 100 parts byweight.
 14. The drilling fluid according to claim 11, wherein thecontent of Pac-Lv is 1 wt % to 3 wt % based on the total weight of thedrilling fluid.
 15. The drilling fluid according to claim 14, whereinthe content of Pac-Lv is 1 wt % to 2 wt % based on the total weight ofthe drilling fluid.
 16. An intelligent temporary plugging typewater-based drilling fluid, wherein the drilling fluid contains two ormore of the following components stored in a mixed manner orindependently: water, sodium bentonite, Pac-Lv, theultralow-permeability agent, calcium carbonate, one-way plugging agent,white asphalt and barite; the ultralow-permeability agent is theamphiphilic block polymer ultralow-permeability agent according to claim10.
 17. The drilling fluid according to claim 16, wherein the content ofthe sodium bentonite is 0.5 parts to 3 parts by weight relative to 100parts by weight of water; the content of the ultralow-permeability agentis 0.5 parts to 3 parts by weight; the content of the calcium carbonateis 2 parts to 8 parts by weight; the content of the one-way pluggingagent is 1 part to 5 parts by weight; the content of the white asphaltis 1 part to 5 parts by weight; the content of the barite is 60 parts to120 parts by weight.
 18. The drilling fluid according to claim 17,wherein the content of the sodium bentonite is 1 part to 2 parts byweight relative to 100 parts by weight of water; the content of theultralow-permeability agent is 1 part to 2 parts by weight; the contentof the calcium carbonate is 4 parts to 6 parts by weight; the content ofthe one-way plugging agent is 2 parts to 3 parts by weight; the contentof the white asphalt is 2 parts to 3 parts by weight; the content of thebarite is 80 parts to 100 parts by weight.
 19. The drilling fluidaccording to claim 16, wherein the content of Pac-Lv is 1 wt % to 3 wt %based on the total weight of the drilling fluid.
 20. The drilling fluidaccording to claim 19, wherein the content of Pac-Lv is 1 wt % to 2 wt %based on the total weight of the drilling fluid.